In the past, there has been a need to control sand or other solids produced from the formation with the flowing oil or other hydrocarbons. Techniques for sand control have involved the use of screens. Various configurations have been attempted for sand-control screens. These screens have generally involved a rigid base pipe which is perforated, overlaid by one or more layers of screen of different opening sizes. Generally, the finest screen, which is the one that is designed for catching the sand or other solid material, is a screen most prone to not only plugging but also other mechanical ailments.
In the past, these fine filtering screens have used very thin wire wrapped around the base pipe and an underlying coarser screen. The filtering screen has generally in the past had a welded longitudinal seam which failed generally due to erosive effects of the flow through the screen or chemical attack on the weldment. Sealing off the ends of the filtering screen to the underlying support structure has also been problematic. Again, due to the fine wire size of the filtering screen, welding the ends to a support body has resulted in failures due to differential expansion creating tensile loads on welds involving fine wire components of the filtering screen. Various mechanical efforts to seal the filtering screen to the underlying structure, such as by use of mechanical bands, has also failed to provide a tight seal, thereby allowing the hydrocarbons to short circuit around the filtering screen, carrying the undesirable sand with them.
In the past, underlying coarse screens below the sand-filtering screen have been made with a wound wire having a triangular cross-section, with a flat side oriented outwardly. This has resulted in coarse screens with fairly small open areas and created numerous dead spots behind the filtering screen where the flat side of the triangularly cross-section wound wire of the underlying coarser screen butted up against the openings of the finer sand-filtering screen. As a result, the sand-filtering screen suffered from losses of efficiency due to the numerous dead spots encountered by the outer flat side of the wound coarse screen broadly abutting the sand-filtering screen.
U.S. Pat. No. 5,611,399 provides a finished assembly that does not suffer from welded attachments to thin members, which had in the past been a weak point in resisting stress, particularly due to tensile loading, flow erosion, as well as chemical attack. It also creates an efficient sand-control screen assembly by employing a substrate of a coarse screen, having wound wires of a more rounded or arcuate cross-section, to reduce the dead zones in between the filtering screen and the underlying coarse screen. It also provides a simple mechanical technique for assembling the elements of the screen.
U.S. Pat. No. 5,611,399 illustrates a sand-filtering screen-making technique which involves an initial assembly of the sand-filtering screen over an underlying coarse screen. The sand-filtering screen has a mechanical longitudinal fold and overlap-type joint. End caps are fitted over the filtering screen which has already been preassembled to the underlying coarse screen. The assembly is then mechanically forced through a die to compress the end caps into the assembled filtering screen and underlying coarse screen. That subassembly is then assembled onto a base pipe and secured. An outer shroud can then be secured to the underlying base pipe, overlaying the filtering screen. The ends of the subassembly comprising the filtering screen and the underlying coarse screen are sealed against the support pipe by a packing gland arrangement at both ends.
This design, although an improvement over prior designs, still had several limitations. Packing glands were required to accommodate relative movement due to thermal effects. This would present potentials for leakage at seals. The crimping assembly, involving overlapping of the ends and folding them over, created a thick longitudinal seam which tended to decrease the given inside diameter for a given outside diameter. The annular gap in such a design, between the outer protective jacket and the filtering components, also limited the differential pressures that could be withstood across this screen.
Thus, some of the objectives of the present invention are to provide a design that could withstand greater differential pressures than prior designs. Another objective is to be able to form the assembly so that the fold overlapping of the prior art can be eliminated, thus enabling the use of a larger inside diameter for a given outside diameter. Another objective is to eliminate the floating end rings used in the prior art and secure the filter directly to a supporting base pipe. Yet another objective is to provide a technique which will allow low-cost manufacturing of the filter assembly. Another objective is to be able to hold the filter media in place with the outer jacket that is pushed on to it in the extrusion process. Another objective is to provide for an assembly that allows for use of nonmetallic components such that in long laterals, the assembly will actually induce buoyancy (cause less drag/friction during installation) to allow it to be more easily advanced into position for subsequent production. These and other advantages will be more apparent to those skilled in the art from a review of the preferred embodiment described below.